Leaf structure and why it matters

Most of the worlds biomass begins production in leaves

Leaves exchange gases via stomata


CO2 IN, O2 and H2O OUT

How stomata work…


- CO2 enters leaf air spaces and then chloroplasts (organelle) through a concentration gradient
- Stomata are not always open….WHY???

Leaf gas exchange impacts the global atmopshere

Vascular tissues in leaves are confined to veins


  • Transpiration (leaf water loss from evaporation) is a by‐product of opened stomatal pores

  • H2O transport needs to be sufficient to keep stomata open

  • Veins represents investment in H2O supply

Angiosperms have evolved higher vein densities


  • Helps explain angiosperm dominance
  • Transpiration alters global climate systems! About 10% of water in atmosphere comes from leaves

Leaf economic theory: Return on Investment

Photosynthesis is complicated….


How do heterotrophs get nutrition for growth?


How do plants get nutrition for growth?

Photosynthesis is the basis for most biomass on Earth




  • Greek = “building with light”
  • Autotroph = “self nourishing”
  • Photoautotroph = “self nourishing with light”


  • Photosynthesis is an energy pathway
    • 2 linked reactions
    • light-dependent reaction + Calvin cycle
    • light reaction makes chemical products for use in the Calvin cycle

Chloroplasts: Where the photosynthetic magic happens

The nature of light




  • Light is a form of energy, characterized by wavelengths


  • Short wavelengths have more energy than long wavelengths


  • Sunlight includes wavelengths in the visible spectrum, UV, and infrared
    • UV is too powerful and infrared to weak for photosynthesis